Background: Dark
tea is one of the most popular types of Chinese
tea, which has been reported to exhibit anti-
obesity, anti-oxidation and antitumor activities in according human cell lines. In terms of
tumorigenesis, the systemic study of the physiological effect of specific fraction of dark
tea and the relevant molecular mechanism warrant more attention. Methods: Dark
tea was firstly isolated through
solvent extraction method. Dissolved
ethyl acetate extract was further fractioned by elution with various concentration of
ethyl alcohol. The cytotoxicity effect of dark
tea on cell proliferation was evaluated by CCK8 assay in HPDE human normal pancreatic duct epithelial cells, SW1990 and PANC-1 human
pancreatic cancer cells, and SW1116 human
colorectal cancer cells. Immunoblotting and flow cytometry analysis were utilized to examine the status of
protein and
reactive oxygen species respectively. Gene expression profile was analyzed by
cDNA microarray and real-time PCR. The plasmid for ID1 expression was stably transfected into SW1990 cells for relevant functional analysis. The effect of dark
tea extract on
tumorigenesis in vivo was studied in xenograft
tumor model. Results: Water eluate fraction of the
ethyl acetate extract from dark
tea inhibited the growth of SW1990, PANC-1 and SW1116 cells more efficiently compared with that in HPDE cells. Meanwhile, p38 activity was increased and AKT activity was dropped in
cancer cells with dark
tea extract treatment. Further functional analyses indicated that water eluate fraction and p38 inhibitor treatment exerted a synergic inhibitory effect on
cancer cells growth, which was related to their suppressive effect on expression level of ID1 (
inhibitor of differentiation protein 1), which was highly expressed in
cancer cells. The analysis utilizing xenograft
tumor model further indicated water eluate fraction exhibited a significantly inhibitory effect on
tumorigenesis. Conclusion: Based on the sequential extraction procedure, our results reveal the inhibitory effect of water eluate fraction of the
ethyl acetate extract from dark
tea and its synergistic effect with p38 inhibition on the growth of
pancreatic cancer cells, in which ID1 is identified as a downstream effector. This sheds insights into the physiological relevance of specific fraction of dark
tea to
tumorigenesis in
pancreatic cancer.